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Lecture 2 - Neuroscience Methods 2 Flashcards

1
Q

What is the purpose of neuroscience techniques

A

Study relationship between brain and behaviour
Idea: spatial resolution cellular temporal resolution ms
Whole brain studied simultaneously = so much data difficult analyse
Non invasive

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2
Q

What is the spatial and temporal resolution for fmri

A

Spatial resolution excellent

Temporal resolution not as good as electrophysiological methods

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3
Q

What is an example of structural imaging

A

MRI

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4
Q

What are the goals of structural imaging

A

Study anatomy
Identify abnormalities
Follow development
Show plasticity

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5
Q

What are the structural imaging methods of interest to Biological psychology

A

Computed tomography CT scans
MRI - Sir Peter Mansfield

Rely on contrast between tissue types white matter vs gray matter vs cerebrospinal fluid

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6
Q

Example of studying juggling in structural MRI

A

Baseline scan
Then juggling boys practice daily until reach certain skill level
After 3 months scanned again

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7
Q

Example of studying juggling in structural MRI results

A

Scan increase grey matter in occipital region

After 3 fourth months told not to practice increase gray matter reversed

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8
Q

What does the study of juggling in structural MRI tell us

A

Brain plasticity after motor learning

Not be confused with fMRI

Correspond area hMT/V5 visual motion area

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9
Q

Outline the extrastriate visual areas

A

Process input from geniculostriate system

V5 = dorsal pathway = vision
E.g. visual coordination grasping

Supported brain structures dorsal pathway

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10
Q

How to generate structural MR contrast

A

Core: magnet generating strong EM field = external static magnetic field. Throughout and around scanner
Outsider scanner protons soft tissues all oriented at random. Undergo spinning movement in random order
Axis oriented vertical axis field. Not random
Protons spin axis generate own MF

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11
Q

How do protons spin axis to generate their own MF in generating structural MR contrast

A

Spin axis not completely vertical rotates about vertical axis
Precessional motion
More protons aligned parallel external (longitudinal) MF
Lower energy than antiparallel

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12
Q

How is 1 cell represented in structural MR contract

A

One cell represented by magnetic vector

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13
Q

What are important components in generating structural MR contrast

A

Radio frequency coils

Scanner

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14
Q

Outline the net magnetisation vector

A

Magnetisation changes in response to radio frequency pulses

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15
Q

Outline use of compass and a magnet in structural MR contrast generation

A

Compass contained surrounding fluid
Beginning points north with earths magnetic field
Magnet applied compass point east
Remove magnet and needle returns

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16
Q

Apply findings of use of compass and a magnet to structural MR contrast generation

A

Protons in bod aligned external magnetic field = net magnetisation
Radio frequency pulse applied
Net magnetisation perpendicular external magnetic field
0% inner magnetic field line with net magnetisation vector
Radio frequency pulse removed net magnetisation vector returns to original state

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17
Q

What is net magnetisation vector

A

Protons body aligned with external magnetic field

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18
Q

How is MR signal measured in MR contrast generation

A

Radio frequency pulse removed net magnetisation vector returns original state
Net magnetisation direction external magnetic field recovers 100% pre radio frequency value
MR signal measured during recovery = readout

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19
Q

What does the MR contrast generation draw on to produce signal

A

Sequences RF pulses and readout = MR protocol

Protons different tissue types gray vs white require different time realign = basis of MR contrast

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20
Q

What happens when you increase vertical component in MR contrast

A

Increase magnetisation
Protons aligned parallel with external magnetic field
That is parallel with external magnetic field
Increase longitudinal magnetisation
Spin lattice relaxation

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21
Q

Outline structure specific time courses of spin lattice relaxation

A

Brain tissue faster relaxation than ventricles CSF T1 signal
Signal brain stronger
MR contrast tissue specific
Radio frequency coil what measures T1

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22
Q

What creates the resulting image in specific time courses of spin lattice relaxation

A

Combination specific radio frequency pulse

Specific readout time

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23
Q

What is the order of contrasts in specific time courses of spin lattice relaxation

A

T1 white matter > T1 gray > T1 CSF

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24
Q

Outline the effects of modifying radio frequency pulses and read out times on MR properties

A

T2 signal white matter < gray matter < CSF

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25
What is the goal of a functional MRI
Identify brain areas support sensory and cognitive processes Derive models brain function
26
What does an fMRI measure
Blood flow | Need contrast separates non activated vs activated tissue
27
What are the 3 problems of fMRIs
How measure neural activity in functional contrast? How generate measurable functional contrast in experiment? How identify functional contrast fMRI raw data?
28
Outline T2 contrast underlying fMRIs for problem 1 how to measure neural activity in fMRI contrast
Depends balance deoxygenated : oxygenated haemoglobin within blood in voxel Then depends on local regulation arterial width Capillaries and arteries carrying blood near inactivate neutron contain both oxygen and deoxygen haemoglobin Near active neuroma predominantly oxygenated
29
Outline local neuronal activation and T2 contrast problem 1 how to measure neural activity in fMRI contrast
Flow increased more oxygen capillaries Diamagnetic = not affect local magnetic field Deoxygenated = paramagnetic field inhomogeneous. T2 signal different oxygenated and deoxygenated blood result. Different time pause
30
What occurs in an inhomogeneous field during local neuronal activation in problem 1 how to measure neural activity in fMRI contrast
Horizontal magnetisation decays fasted (T2 decay) Slower T2 decay increased MR signal Blood oxygen dependent = BOLD effect
31
Outline role of BOLD signal in problem 1 how to measure neural activity in fMRI contrast
Blood oxygen level dependent | Indirect measure neural activity
32
Problem 2 how to generate functional stimulus related contrast
Radio frequency coil seeks excitation Watch display on checkerboard When stop watching and look away increase amplitude MR signal
33
Problem 2 how to generate functional stimulus related contrast application to an experiment
Visual cortex max BOLD signal 6 secs after visual stimuli Temporal delay means fMRI poor temporal resolution 24 secs per trial 2% signal change time Peak responses only 4% higher than base
34
Outline spaced event related design to increase signal fMRI and address Problem 2 how to generate functional stimulus related contrast
Improve contrast and noise | Design types differ in temporal sequence stimuli
35
Outline rapid event related design to increase signal fMRI and address Problem 2 how to generate functional stimulus related contrast
Stimuli e.g. category A and B Immediately success each other with short diagnosis Non correlated time cause it to become possible separate responses
36
Outline block design to increase signal fMRI and address Problem 2 how to generate functional stimulus related contrast
All stimuli and responses external event grouped in blocks E.g. 20 secs baseline, 20 secs rest Increase functional contrast:noise ratio Responses to individual events within blocks and alert stronger signal
37
Outline advantages of BLOCK design
BOLD effect additive more stimuli = more signal Good statistical power Robust Continuous activation
38
Outline disadvantages of BLOCK design
Stimuli predictable = unsuitable many tasks Inflexible Limited number conditions
39
How to address the problem of overlapping BOLD responses in Event related designs
Long stimulus intervals | Each type response unique time course - randomised ISI or randomised trial types
40
Advantages of Event Related Designs
Avoids habituation | Analyse subtypes responses
41
Disadvantages of Event Related Designs
Reduced sensitivity to neural events
42
Aims of experimental design for fMRI
``` Optimise contrast : noise Measures contrast of interest Baseline well controlled Attentional effects controlled Duration ```
43
What are the spatial pre processing steps of fMRI to identify areas that show functional contrast
Motion correction Co-registration between subjects fMRI and anatomical scans Normalisation: warp scans from different individuals Spatial smoothing
44
Outline why the pre processing of motion correction to identify areas that show functional contrast has to occur
FMRI lasts 5-10 mins Few subjects keep head in same position throughout Spatial resolution 3mm movement interferes
45
Outline the steps or motion correct and co registration for pre processing of fMRI
Motion correction; Align each volume of brain to target volume Detect and correct movement Co registration BOLD results superimposed high resolution structural image
46
Outline pre processing of Normalisation of fMRI
Subject 1 and 2 may have different head positions or different head shapes Normalisation -> template -> average activation
47
Does motion correction help with between or within or single subjects
Single subjects | Within subject
48
Does normalisation help with between or within or single subjects
Between subjects
49
Problem with pre processing step of normalisation
Belief everyone’s brain match to 1 template Lot variability Caveat: sulcal variability
50
Outline Pre processing normalisation for comparison with anatomical template
Compare location in individual subjects Example: location shows activation and has prior located in cordinal system Get values for XYZ
51
Limitations Pre processing normalisation for comparison with anatomical template
Only 1 brain 1 hemisphere Fixation likely changed shape brain
52
What data do you compare in block design
Compare signal rest with signal during blocks stimuli Observed time course compared predicted time course = SCHEMATIC Look voxels where predicted time course and observed time course shows good match
53
Disadvantages of fMRI
Low power Type 1 errors false positives Null results impossible interpret Do not justify region not involved Stat maps depend on amplitude and noise
54
What is phantom limb pain
Patient undergone amputation limb | Frequently reports sensation from lost limb
55
Can myoelecteic prosthesis prevent cortical reorganisation and phantom limb pain - Lotze et al 1999
Injury, stimulation or training induce changes homuncular organisation primary motor cortex Change cortical periphery brain this lost limb Phantom limb = Perceptual correlate cortical reorganisation
56
What happens when there is enhanced used of myoelectric prosthesis in phantom limbs
Reduced phantom limb pain | Reduced cortical reorganisation
57
What is the Albert Task
Patient cross out all lines on sheet paper
58
What are the effects of brain lesions on the Albert Task
Only crossed out lines to right half paper
59
What is the line bisection task
Mark bisection point middle point of each line
60
What are the effects of brain lesions on the Line Bisection Task
Patient chooses bisection point shifted to the right
61
Outline the Drawing Task
Copy picture drawing Shown image 2 flowers asked draw From previous experiments expect ppts only draw right hand flowed
62
What are the effects of brain lesions on the Drawing Task
In fact drew only the right hand half of BOTH flowers Left remained blank Flowers incomplete
63
What tasks assess brain anatomy
Albert task Line bisection task Drawing task
64
What is the goal of neuropsychology
Relate brain anatomy to behaviour CT MRI functional localisation Localise impaired behaviour to damaged regions - lesion May affect relay station rather originally functional region Exclude localisation preserved skills to damaged regions. Other regions may have reorganised perform functions originally localised to damage region
65
Example of neuropsychology relating brain anatomy to behaviour
Association: damage single brain region but multiple deficits. Syndrome Dissociation: damage leads impaired performance in task A bit performance Task B normal
66
What is an Association
Damage single brain region but multiple security Require same neural circuit Or Separate functional regions are anatomical neighbours Or Area common relay station for anatomically functionally distinct regions
67
Outline the example of studying Associations Balints Syndrome
Simultanagnosia - only perceive one item at time Deficit of perception Oculomotor apraxia failure make eye movements Back and forth between 2 points Outlining perimeter Optic ataxia - inability reach seen target
68
What Disorder is associated with studying dissociations
Visual form agnosia Ventrolateral occipital lesion
69
What are the two tasks to test visual form of agnosia
Posting task Perceptual matching task
70
Outline the posting task
Putting envelope through slot that can be rotated
71
Outline performance in someone with visual form agnosia in posting task
Perform reasonably well | But not good as controls
72
Outline the perceptual matching task
Without hand movement | Judge whether lines horizontal or vertical
73
Outline performance in someone with visual form agnosia in perceptual matching task
Large differences between patients and controls
74
Why are their apparent differences in the posting task and perceptual matching task with visual form agnosia
Difference between visual form to guide movements (posting task) Vs visual form to recognise objects (perceptual matching task)
75
What brain regions can account for the differences in performance with those with visual form agnosia
Visual form guide movements: dorsal stream Recognise objects, orientation: ventral stream Deteriorated visual recognition and ventral stream
76
What is a dissociation study
Patient impaired in one task but performs normally in different task
77
Why does the interference occur in dissociation task
Impaired task more difficult? | Performance unimpaired task at ceiling?
78
Outline visual agnosia patients performance in discriminating shapes visually
Poor Failed complete objects outline Inability recognise line drawings or shapes
79
Outline visual agnosia patients performance in grasping irregularly shaped objects
Good
80
Outline optic ataxia patients performance in discriminating shapes visually
Good
81
Outline optic ataxia patients performance in grasping irregularly shaped objects
Poor Unable use visual info about object shape to control movement Difficulty pointing or grasping movements Symptom Balints Syndrome
82
Why does Goodale et al 199 believe there are differences in optic ataxia and visual agnosia patients
Different brain circuits for visual perception vs visual control of skilled action
83
What are the effects of visual pathway lesions to ventral stream
Poor visual shape discrimination Good visually guided movement
84
What are the effects of lesions to dorsal stream
Good visual shape discrimination Poor visually guided movements
85
Outline step 1 for measuring double dissociation for right frontal lobe lesions impairing memory for designs vs words
1st compare same right frontal region with controls Right frontal lesion poorer performance memory designs Double dissociation - compare controls right and left frontal lesions
86
Double dissociation for right frontal lobe lesions impairing memory for designs vs words findings
Left frontal lesion worse for memory words Non overlapping component operations Poor memory designs due to unspecific attention deficit
87
Outline limitation that variation in pathologies makes group studies difficult
``` Inference from single patients weak Lesion size and location variable Hard find similar patients Normalisation scans weakens anatomical inference Functional anatomy variable ```
88
Outline effects of lesion size on behavioural outcome
Small lesions = little effects. Robust partial damage Small lesions strategic locations = deficit Large lesions = damage several centres Reorganisation: intact regions change behaviour
89
How can limitations be overcome
Combining different methods with complementary strengths

Neuroscience (12 decks)

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